The invention relates to guidance devices for selfpowered vehicles and more particularly to a power steering guidance device for an order picking vehicle or the like.
In the material handling industry, high-rise order picker vehicles (OPVs) permit narrow aisle storage and retrieval operations of nonpalletized case or item storage. Such OPVs carry an operator on a lifting platform who picks orders from either a pallet or a storage module. The lifting platform incorporates the vehicle control so the operator can ride on the platform. The aisle widths are extremely narrow and may be as narrow as four feet. It is thus desirable that the operator have accurate control of the vehicle's steering. Such control preferably involves a power steering mechanism but the cost of conventionally converting existing OPVs to power steering is quite high. Another problem is that in some circumstances it is preferable to allow the operator to override the power steering control, such as in some emergency situations. Some prior art built-in systems make no provision for this feature. The consideration of an automatic guidance mode raises still other problems.
If the vehicle is guided other than by the operator down the aisle, it is safe for him to drive forward while the platform on which he is standing is being elevated. Otherwise, in nonguided aisles, the driver must first drive to the proper location and then activate the lift. This feature of moving forward while elevating, called "overlap" in the material handling industry, significantly improves operator productivity. Industrial safety codes in many states do not permit overlap unless the vehicles are guided in the aisle other than by the operator. OPV guidance, then, not only achieves increased storage capacity by minimizing aisle widths, but it also increases labor productivity by speeding up picking times.
There are basically two types of prior art guidance systems for OPVs. In the first type the OPV is mechanically guided. Rollers attached to the vehicle make contact upon aisle entry with steel rails bolted to the floor on either side of the aisle. The operator controls speed, stops and starts, and the vehicle is centered in the aisle mechanically. Although mechanical guidance systems offer economy and some degree of flexibility over the electronic guidance systems to be discussed hereinafter, the mechanical guidance systems have several disadvantages, such as high maintenance cost, rough operation, and excessive space requirements.
Many of the above disadvantages of mechanically-guided OPVs are overcome by fully electronic guidance systems in which a wire is buried in the floor of the storage facility and specialized sensing positioning units are built into the OPV to follow along the buried wire. Such specially-built OPVs may run as much as $50,000 to $75,000, which is many times more expensive than mechanically-guided OPVs. Most of such electronic systems are completely automated, that is the vehicle is under automated control all of the time. Because of this enormous expense, mechanical guidance, at the present time, has nearly all of the OPV guidance market. One advantage of electronic guidance is that it minimizes vehicle down time and maintenance expense due to mechanical damage to equipment. This is because in the electronic guidance system, the OPV is actually steered down the aisle rather than being mechanically forced into position.